Thousands of soldiers will move to new units — and the Army’s primary fighting formations will undergo a massive overhaul — in one of the service’s largest organizational changes since World War II.

The Army will cut 10 brigade combat teams and reorganize the rest as it shrinks the active-duty force from a wartime high of about 570,000 to 490,000, Army Chief of Staff Gen. Ray Odierno said June 25.

The reorganization — scheduled to begin in October, the start of fiscal 2014, and be completed by the end of fiscal 2017 — takes place as the Army transitions from more than 12 years of war in Iraq and Afghanistan. The force reduction is the result of the Budget Control Act of 2011, and Odierno warned that sequestration could bring deeper cuts in the future.

The Budget Control Act requires a mandatory $487 billion reduction in spending; the Army’s share of that between now and 2020 is $170 billion.

“This is the new Army,” Odierno said during a town hall meeting June 26 with troops at Joint Base Lewis-McChord, Wash. “The new Army is something that is globally responsive and regionally engaged. We have to be able to respond anywhere in the world very quickly.”

In addition to these 10 BCTs, the Army has announced the inactivation of two BCTs in Germany — the 170th and 172nd BCTs.

This will leave the Army with 12 armored BCTs, 14 infantry BCTs and seven Stryker brigades, a critical consideration as the Army determined which BCTs should be cut.

In the future, another BCT, this one overseas, will be identified for inactivation, Odierno said, bringing the final number of BCTs to 32.

The Army also will reorganize most of its remaining BCTs by adding a third maneuver battalion to its armored and infantry brigades. The Army’s Stryker brigades each has three maneuver battalions, and the BCTs stationed outside the continental U.S. — four in all — will remain at two maneuver battalions for now, mostly as a way to save on military construction costs, officials said.

The move enables the Army to retain 95 of its 98 combat battalions across the BCTs while eliminating headquarters and staff elements.

The BCTs will receive additional engineer and fires capabilities.

Infantry and Stryker BCTs now have one engineer company, while armored BCTs have two, officials have said.

Under the reorganization, the brigade support troops battalion in each BCT will be converted into a brigade engineer battalion, said Maj. Gen. John Murray, director of force management in the Army G-3 (operations).

The engineer battalions will have gap-crossing and breaching capabilities, as well as route clearance assets, Murray said.

This would expand the number of engineers in each brigade from about 120 in the infantry and Stryker BCTs and about 200 in the armored BCTs to more than 300 engineers in all.

The BCTs also will have increased fires capability by going from a 2-by-8-gun fires battalion to a 3-by-6, Murray said. This gives the brigades two additional guns and one additional battery to support the three maneuver battalions, he said.

These changes will make the Army’s remaining BCTs “more lethal, flexible and agile,” Odierno said.

Once the reorganization is completed, each BCT will have about 4,500 soldiers, nearly 1,000 more than they do in their current configuration.

The decision to reorganize the BCTs came after extensive analysis, lessons learned from 12 years of war, and the need to increase the Army’s operational capability and flexibility, Odierno said.

The Army conducted an “extensive” analysis that included more than 6,500 hours of simulated combat, interviews with commanders, an environmental analysis, and listening sessions at 30 installations across the country.

The Army also deferred $788 million in military construction projects until these decisions were made, and officials expect to cancel almost $400 million in projects permanently as the BCTs reorganize, Odierno said.

Choosing which units to inactivate was difficult, Lt. Gen. James Huggins, deputy Army chief of staff for operations, told Army Times. The Army looked for places that could transfer soldiers without moving them, and places where the existing infrastructure would support the larger units, as newly designed BCTs will increase in size from about 3,500 soldiers to about 4,500, he said.

Most soldiers from the 10 BCTs slated for inactivation likely will be absorbed into the remaining — and growing — BCTs. It also is likely, on an installation as large as Fort Bragg or Fort Hood, for example, for most soldiers to be moved into new units without a permanent change of station.

The Army also will try to retain “as many of the regimental colors as we can,” said Vice Chief of Staff Gen. John Campbell.

In all, the BCT cuts will result in the loss of about 17,700 positions, Campbell said. The inactivation of the two BCTs and several smaller enabler units in Europe represent a reduction of about 11,700 slots, he said.

“The BCT reduction is just one small part” of the 80,000-troop reduction in end strength, he said.

The reorganization and force structure cuts ensure the Army doesn’t become “hollow and unready,” Murray said.

“Whether we change the structure or not, we’re going to end up with 490,000 soldiers,” he said. “What this is about is adjusting the structure to match the spaces to the faces, because if you don’t do that, you end up with over-structure, and you end up with units being manned at 60, 70, 75 percent.”

The Army must continue to maintain a high level of readiness even as the cuts take place, Odierno said during the town hall meeting at Joint Base Lewis-McChord, which is losing one of its Stryker brigades.

Even with fewer BCTs, the Army will regionally align its forces with combatant commands around the world, and soldiers will be given the opportunity to deploy to more places for shorter periods of time to “prevent conflict, to shape the area,” he said. Soldiers must “move to an expeditionary mindset,” Odierno said.

“The reality is, when we were deploying to Iraq and Afghanistan, we were deploying to very mature infrastructure,” he said. “When I talk about an expeditionary mindset, [I mean] the ability to deploy in small packages to remote areas that have very little infrastructure, where we have to be able to communicate very quickly, where we have to be able to survive with very little support. It’s important we understand that as we go forward.”

The active Army will cut 80,000 soldiers by 2017, a reduction of about 14 percent of the force. Most of the reductions will take place through natural attrition, Odierno said, but the Army also will conduct boards for select lieutenant colonels and colonels, as well as captains in certain over-strength year groups.

The National Guard will go from 358,000 to 350,000 and the Army Reserve will remain at 205,000.

When asked why the active Army appears to be taking the deepest cuts, Odierno said most of the wartime growth took place in the active component.

“When we were involved in Iraq and Afghanistan, the large majority of the increase happened in the active component,” he said. “As we reviewed the new defense strategy, we believed it was more appropriate … that we reduce the active component to 490,000. As we move forward, we have to do more of a balance, because in my mind, there’s a role we each play.”

What has not been decided is what will happen to the Guard’s 28 BCTs, which are configured the same way as active Army BCTs.

“Whatever the Army has in structure, our goal is to look like that Army structure,” said Gen. Frank Grass, chief of the National Guard Bureau. “But it’s too early to tell what the outcome will be yet. We’re still in discussions and we’re a long way from any decisions at this point.”

The announcement of the Army’s sweeping reorganization ignited furious debate on Capitol Hill and in the communities that depend on nearby military installations as a key part of their economy.

Reaction from Capitol Hill was swift, with Senate Armed Services Committee ranking member Sen. James Inhofe, R-Okla., saying the Army’s plan “[is] putting us so close to a hollow force that that’ll be the next announcement you hear.”

“I’m not sure they have much choice,” Levin said, citing defense spending caps etched in stone by the 2011 Budget Control Act. “They’ve got to find a way to implement the law that was passed by Congress.”

Other lawmakers, such as House Armed Services Committee member Rep. Doug Lamborn, R-Colo., were relieved that the cuts to installations in their states weren’t worse.

“I am very disappointed that Fort Carson is one of ten bases around the country that will lose a brigade combat team by the year 2017,” Lamborn said in a statement. “However, the blow is considerably softened by the fact that all but 750 of those soldiers will remain at Fort Carson and be reassigned to other missions.”

The Army anticipates that Fort Carson’s population will increase by 1,800 active-duty personnel in coming years.

The Army took into consideration the impact of these cuts on the local communities, Odierno said.

“We’ve spread it out quite well,” he said. “We maintain forces on the West Coast, forces in the Midwest, [and] forces on the East Coast. The way we took out brigades reduces the impact. The only outlier is Fort Knox, where there’s only one brigade there.”

The Army also looked at each installation’s capabilities, Murray said.

Fort Bliss, as an example, has massive training space and premier training facilities well suited for armored brigades, which is why the infantry brigade there was selected for inactivation instead of the others, he said. The 1st Armored Division will retain one Stryker brigade and two armored BCTs.

Commanders at the affected installations said they remain focused on their mission.

“Fort Drum remains one of the newest, most sustainable, state-of-the-art installations in our nation’s Army,” Maj. Gen. Stephen Townsend, commander of the 10th Mountain Division and the New York post, said in a statement.

The division’s 3rd BCT, which was activated in September 2004, is one of the 10 BCTs that will be cut. The brigade has deployed three times to Afghanistan, and anticipates at least one more deployment before it is inactivated, Townsend said.

He also said he doesn’t expect the overall reduction in troops to have a “significant impact” on Fort Drum as the remaining brigades are reorganized.

“We expect the net loss to be somewhere between 1,500 and 2,000 soldiers,” he said.

Fort Hood, home to the 1st Cavalry Division, which will inactivate its 4th BCT, will likely see a net loss of about 2,900 soldiers by 2017, Maj. Gen. Anthony Ierardi, senior commander of III Corps and Fort Hood, said in a statement.

“Fort Hood will remain an essential power projection platform and home to multiple major operating force units and force generating capabilities,” Ierardi said.

Leaders for 4th Stryker Brigade Combat Team, 2nd Infantry Division, which is slated for inactivation, are focused on the 2,000 soldiers from the unit who are deployed to Afghanistan, said Lt. Col. Joe Sowers, spokesman for the 7th Infantry Division, which provides command and control to the brigade.

“We’re focused on supporting 4th SBCT units that are downrange right now in any way we can,” Sowers said. “And when they start to come back, our next focus becomes reintegrating them with their families and the JBLM community.”

Once the inactivation gets underway, Sowers anticipates it’s “going to be a complex balancing act.

“We’re going to have to be deliberate about it, taking the needs of the Army, the needs of the soldier, the needs of the family, as we progress through,” he said. “There’s a lot of planning and decisions that are still yet to be made.”

The 1st Infantry Division is the only division to have two BCTs slated for inactivation — its 3rd BCT at Fort Knox, which is deployed, and 4th BCT at Fort Riley.

“This force structure ensures the 1st Infantry Division remains on point for our nation well into the future and ensures the Army’s adaptability and flexibility,” Maj. Gen. Paul Funk, the division commander, said in a statement. “I can assure you that the entire team here is committed to mitigating — as much as humanly possible — the impact this announcement and its implementation will have on our soldiers, our families and our communities.”

Staff writers Paul McLeary and John T. Bennett contributed to this report.